Android应用开发学习之画廊视图

作者：刘昊昱

博客：http://blog.****.net/liuhaoyutz

画廊视图Gallery能按水平方向显示一组图片，并可以拖动图片。下面我们来看一个使用画廊视图的例子，其运行效果如下：

先来看主布局文件main.xml，其内容如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="20px"
        android:text="@string/hello" />

    <Gallery
        android:id="@+id/gallery"
        android:spacing="5px"
        android:unselectedAlpha="0.5"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

下面看主Activity文件，其内容如下：

package com.liuhaoyu;

import android.app.Activity;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */
	private int[] imageId = new int[] { R.drawable.img01, R.drawable.img02,
			R.drawable.img03, R.drawable.img04, R.drawable.img05,
			R.drawable.img06, R.drawable.img07, R.drawable.img08};

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Gallery gallery = (Gallery) findViewById(R.id.gallery);

		BaseAdapter adapter = new BaseAdapter() {
			@Override
			public View getView(int position, View convertView, ViewGroup parent) {
				ImageView imageview;
				if (convertView == null) {
					imageview = new ImageView(MainActivity.this);
					imageview.setScaleType(ImageView.ScaleType.FIT_XY);
					imageview.setLayoutParams(new Gallery.LayoutParams(180, 135));
					TypedArray typedArray = obtainStyledAttributes(R.styleable.Gallery);
					imageview.setBackgroundResource(typedArray.getResourceId(
							R.styleable.Gallery_android_galleryItemBackground,
							0));
					imageview.setPadding(5, 0, 5, 0);
				} else {
					imageview = (ImageView) convertView;
				}
				imageview.setImageResource(imageId[position]);
				return imageview;
			}

			@Override
			public long getItemId(int position) {
				return position;
			}

			@Override
			public Object getItem(int position) {
				return position;
			}

			@Override
			public int getCount() {
				return imageId.length;
			}
		};
		gallery.setAdapter(adapter);
		gallery.setSelection(imageId.length / 2);
		gallery.setOnItemClickListener(new OnItemClickListener() {
			@Override
			public void onItemClick(AdapterView<?> parent, View view,
					int position, long id) {
				Toast.makeText(MainActivity.this,
						"第" + String.valueOf(position+1) + "张图片被选中",
						Toast.LENGTH_SHORT).show();
			}
		});
    }
}

在res/values目录中，创建attr.xml文件，该文件用于自定义属性，其内容如下：

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="Gallery">
        <attr name="android:galleryItemBackground" />
    </declare-styleable>
</resources>